Re: Re: [PATCH] linedit, deluser: use POSIX getpwent instead of getpwent_r

[Rich Felker <dalias@libc.org>]

On Mon, Feb 09, 2015 at 01:05:07PM -0500, M Farkas-Dyck wrote:
> On 07/02/2015, Rich Felker <dalias@libc.org> wrote:
> > On Sat, Feb 07, 2015 at 03:14:10PM +0100, Denys Vlasenko wrote:
> >> On Sat, Feb 7, 2015 at 2:32 AM, Rich Felker <dalias@libc.org> wrote:
> >> >> > the _r functions are for thread-safe
> >> >> > versions of their corresponding legacy functions, but getpwent_r has
> >> >> > inherent global state -- the iterator. Whoever made it just wasn't
> >> >> > thinking. To make a correct interface like this the caller would
> >> >> > need
> >> >> > to have an iterator object to pass to the function, but I can't see
> >> >> > much merit in inventing a new interface for this.
> 
> buf may contain arbitrary data, yes? If so we could store the iterator there.

No. On entry the buffer must be assumed to be uninitialized. The
caller could be passing a completely new buffer each time, and even if
not, on the first call the buffer is going to contain junk. The
contract of getpwent_r, at least on glibc and compatible systems,
seems to be that it uses the same iterator as getpwent. But since it
turns out there are multiple incompatible historical functions names
getpwent_r that all behave differently, this proposal has basically
been shelved anyway. Busybox has dropped its use of getpwent_r.

Rich